The present invention relates to a speed transmission for a mower, particularly for lawns, that is self-propelled, with a variable speed of advance.
It relates more particularly to a transmission between the primary motor shaft that carries the mowing blade, with a constant speed of rotation, of a lawnmower and the output shaft of a reducer coupled to the wheels of the mower.
The invention also relates to a mower, in particular for lawns, provided with such a transmission.
Self-propelled lawnmowers, also called traction lawnmowers, generally have, for basic models, a constant speed of advance. For more developed models, these self-propelled lawnmowers are provided with a gearbox. There results a substantial increase in the cost of the mower accompanied by the risk of more frequent breakdown. Moreover, the design of lawnmowers, in particular the length of the blade-carrying motor shaft, at present limits the solutions to be foreseen, by reason of available space. Solutions with a transmission belt have been imagined to provide a speed variation. However, in this case, the transmissions are constituted by at least three successive pulleys, the intermediate pulley constituting a relay pulley. It is accordingly necessary to have at least two belts to ensure transmission. Because of this, the risk of breakdown is again multiplied.
There is moreover known a belt transmission with variable speed, in which the speed variation is obtained by means of a driven pulley whose flanges are controlled manually as to their spacing. In this case, such a transmission is arranged to coact with a power-driven pulley with a fixed flange, a tensioning roller ensuring the tension in the belt. This solution is more particularly described in U.S. Pat. No. 4,117,652.
There is another category of transmissions in which the drive pulley is adapted to ensure speed variation and to coact with a driven pulley.
In short, it can therefore be considered that until now there are two types of transmissions:
a first transmission type in which the driven pulley provides for speed variation and coacts with a drive pulley with fixed flanges,
a second transmission type in which the drive pulley ensures the variation of speed and coacts with a driven pulley with flanges that are fixed or not.
However, in the case of an application to lawnmowers, the region adjacent the blade-carrying motor shaft is a dangerous region because of the presence of a rotating blade. It is accordingly impossible to have delicate members on this motor shaft. At present, solutions are being sought that will permit the production of a transmission for self-propelled lawnmowers with variable speed of advance, at a low cost.
An object of the present invention is to provide a speed transmission for self-propelled lawnmowers with a variable speed of advance and a wide range of variation of speed, whose design is particularly simple and of reduced cost.
Another object of the present invention is to provide a transmission of the mentioned type, which permits reducing the forces exerted on the members constituting the driven pulley.
Another object of the present invention is to provide a transmission of the mentioned type, of small size and whose assembly of fragile members is disposed at a distance from the working zone of the mower blade.
Another object of the present invention is to provide a speed transmission of the mentioned type, whose control force can be moderated because it is proportional to the force produced by the drive pulley.
Another object of the present invention is to provide a transmission whose range of speed variation is wide.
To this end, the invention has for its object a speed transmission for mowers, particularly lawnmowers, that is self-propelled with a variable speed of advance, between the primary motor shaft that carries the mower blade at a constant speed of rotation and the output shaft of a reducer coupled to the wheels of the mower, this transmission having, upstream of the reducer disposed preferably within a housing, a speed changer between the primary motor shaft that carries the blade and the input shaft of the reducer, characterized in that the speed changer is constituted by a belt transmission between a drive pulley adapted to be mounted on the blade-carrying motor shaft and a driven pulley adapted to be mounted on the input shaft of the reducer, the drive pulley and the driven pulley each comprising flanges movable toward and away from each other, the movement of the flanges of the drive pulley, ensuring the permanent tension in the belt, being controlled automatically as a function of the couple transmitted between said pulleys by means of a member for the continuous adjustment of the tension of the belt, positioned adjacent this pulley, whilst the movement of the flanges of the driven pulley, ensuring speed variation, is controlled manually, by means of a control member positioned immediately adjacent the reducer to be isolated from the cutting field of the blade and to be protected from abrasive projections and fowling in the working zone.
Thanks to the design of this transmission, the control force is moderate because it is proportional to the force produced on the drive pulley and the control cable is no longer adjacent the mower blade, such that any risk of breaking this cable by the blade is avoided.
Moreover, the risk of breakdown of such a transmission, because of the presence of a single belt, is reduced without reducing the range of speed variation, which is wide.
Finally, the assembly of the members disposed on the driven pulley or receiver is not subject, because of the presence of a member for continuously adjusting the belt on the drive pulley, to forces that are too great, which limits the wear on said members.
Finally, such a design associating two variable pulleys permits obtaining a wide range of speed variations, the two pulleys taking part in this speed variation whilst being free from a tensioning roller. Moreover, the design of this transmission permits, in the absence of action on the control device of the drive pulley, obtaining a rapid speed transmission. The control device thus permits the passage of the transmission from a rapid speed to a low speed. This solution is particularly advantageous in the case of transmission for lawnmowers, because the rapid speed is the one most used. This solution results again from the positioning of the pulley ensuring speed variation.
The invention also has for its object a self-propelled lawnmower with variable speed of advance, characterized in that it comprises a transmission of the above type.